Skip reentry is a technique for the controlled entry of a space vehicle into the atmosphere of a planet. The technique involves one or more successive “skips” off the atmosphere of the planet to achieve a greater entry range and/or to slow the space vehicle before final entry. This can be advantageous, for example, to control the location of entry of a space vehicle into a planetary atmosphere, and to decrease the significant amount of heat energy that is generated on the surface of the vehicle during its descent through the atmosphere. The control of the range of the space vehicle afforded by skip reentry can allow the vehicle to reach a landing area further down range from the initial entry point, and/or to reach a designated landing point from a wider range of possible entry times. This may be of particular importance, for example, in abort situations.
In order to perform a skip reentry maneuver, precise guidance of the vehicle is required. For example, if the entry angle is too shallow, the velocity of the vehicle may not be sufficiently reduced to allow for reentry; whereas, if the entry angle is too steep, excessive heating and stress may be imposed on the vehicle structure which could exceed the design limits of the vehicle and result in possible damage or even catastrophic failure of the vehicle structure.
The basic method required for skip reentry is to have the vehicle enter the atmosphere at such an angle, and with sufficient lift, that the forces produced on the vehicle by the atmospheric boundary have the effect of pushing the vehicle back out into space. This process can be repeated a number of times, with the vehicle's velocity being reduced with each successive “skip,” in order to control the location and flight conditions of the vehicle upon its final entry into the atmosphere.
Basic skip reentry techniques were utilized by the Soviet unmanned Zond space missions of the 1960s, and were evaluated by NASA, for example during the U.S. Apollo program of the 1960s and 1970s, and more recently in the Space Shuttle program. However, prior methods of performing atmospheric skip trajectory shaping, including the methods developed for the Zond, Apollo, and Space Shuttle programs, have been limited to the use of aero-guidance techniques only. This has, as a result, significantly limited the potential range and targeting precision available to space vehicles performing skip reentry maneuvers.